A member of Nobel Peace Prize winner Rigoberta Menchu's party was shot dead on Tuesday

Amnesty International has called on all candidates in the upcoming elections in Guatemala to renounce violence after a spate of killings in the country.

More than 40 local candidates, party workers and activists have been killed in the bloodiest campaign since the civil war ended in 1996.

In an open letter, the human rights group urged candidates to respect human rights and the rule of law.

The country will hold congressional and presidential elections on 9 September.

Amnesty blames the crisis on a failure to hold to account those responsible for thousands of murders and incidents of torture during the country's 36-year civil war.

In the letter, deputy director of Amnesty's Americas programme Kerrie Howard argued that this had caused a "proliferation of clandestine groups who operate with absolute impunity".

She added that many of the groups had infiltrated state institutions.

'Message'

The most recent victim of the violence was killed on Tuesday.

Clara Luz Lopez, a centre-left political candidate who was running for a local council seat in the south-east of Guatemala, was shot dead while driving home after campaigning.

She was a member of the party of Rigoberta Menchu, the Nobel Peace Prize winner who is standing for president.

"This is a clear message for our candidates and for us," said Ms Menchu, the first Mayan woman to run for the presidency in Guatemala.

Earlier this month, the deputy head of a team of EU election monitors in Guatemala said his delegation was concerned that the violence would have a detrimental effect on the election and could tarnish the final result.

So far there have been no arrests in connection with the killings, which have not been aimed exclusively at any of the leading political parties.

Guatemala has one of the world's highest homicide rates, with close to 6,000 people killed in the country of 13 million last year.

Prosecutors have warned that it is not entirely clear whether all the killings have been politically motivated.